Researchers Find Some Volcanoes 'Scream' At Increasing Pitches Until They Blow 59
vinces99 writes "Swarms of small earthquakes often precede a volcanic eruption. They can reach such rapid succession that they create a "harmonic tremor" that resembles sound made by some musical instruments. A new analysis of an eruption sequence at Alaska's Redoubt Volcano in March 2009 shows the harmonic tremor glided to substantially higher frequencies and then stopped abruptly just before six of the eruptions. Scientists at the U.S. Geological Survey's Alaska Volcano Observatory have dubbed the highest-frequency harmonic tremor at Redoubt Volcano 'the screams' because the episodes reach such high pitch compared with a 1-to-5 hertz starting point. Alicia Hotovec-Ellis, a University of Washington doctoral student in Earth and space sciences and an author of two papers examining the phenomenon, has created a 10-second recording and a one-minute recording that provides a 60-times faster representation of harmonic tremor and small earthquakes."
Makes sense, fluid dynamics and all that... (Score:5, Interesting)
How many db? (Score:5, Interesting)
Re:Up into the human range (Score:4, Interesting)
At their peak, just before they blow, these "screams" get to a high enough frequency that humans could hear them. Of course, to us it would sound like a low frequency rumble.
In other words, if you are standing on a volcano, and start to hear it grumble, get away. Fast.
About 12 years ago there were swarms of tremors around the Long Valley, near Mammoth Mountain, California. 600-800 earthquakes per day from sub 1.0 to 3.0+ and elevation changes around the caldera indicated pressure was building. Then suddenly nothing happened and they subsides. Still a few here and there, but some activity took place and then ended. Massive false alarm or very long range warning? You scare a lot of people with eruption talk, which doesn't materialize, and you'll have most of them home when it suddenly goes BOOM without warning.